<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>测试1</title>
    <style>
        .div0{
            margin: 0 auto;
            height:750px;
            width: 750px;
            border:10px solid blue;
            line-height:1030px;
            text-align:center;

            border-radius: 50%;
        }
        .redBox{
            display:inline-block;
            width:300px;
            height:300px;
            border: 10px solid red;

            border-radius: 50%;
        }
    </style>
</head>
<body>
<div class="body">
    <div class="within">
        <div class="div0">
            <div class="redBox"></div>
        </div>
    </div>

</div>


</body>
</html>